This invention relates to superconductor structures in general and more particularly to a cable shaped cryogenically stabilized heavy current superconductor structure.
A cable shaped cryogenically stabilized heavy current superconductor structure which contains superconducting elements comprising strands of superconductive material which are embedded in a matrix material of predetermined electric conductivity, with several stabilizing elements of thermally and electrically highly conductive material extending parallel thereto is described in U.S. Pat. No. 4,195,199. The stabilizing elements are normally electrically normally conducting at the operating temperature of the superconductor structure, and have an electric conductivity which is substantially higher in the normally conducting state of the heavy current superconductor structure than that of the matrix material of the superconducting elements. Also included is a support body of a material of relatively low thermal and electric conductivity, on which the stabilizing elements and the superconducting elements are fastened.
The superconductive material of the superconductive strands of the corresponding elements of this known current superconductor structure may be, in particular, an intermetallic compound of the type A.sub.3 B with an A-15 crystal structure as for instance Nb.sub.3 Sn or V.sub.3 Ga. The elements therefore each contain a multiplicity of filaments of such an intermetallic compound embedded in a bronze matrix. Such heavy current superconductor structures have good superconducting properties, are distinguished by high critical values and are therefore suitable particularly for magnet windings to generate strong magnetic fields. Besides the mentioned superconducting binary compounds, ternary compounds such as niobium-aluminum-germanium Nb.sub.3 Al.sub.0.8 Ge.sub.0.2 may also be provided as conductive materials.
To ensure undisturbed continuous operation of a device equipped with superconductor structure such as a magnet coil or a cable, so-called cryogenic stabilization may be provided. According to this well-known type of stabilization, the superconductive material of the conductor is joined to electrically and thermally highly conductive material such as copper or aluminum. By thoroughly cooling this normally conducting material, a spot in the superconductive material which has become normally conducting can be returned to the superconducting state without interruption of the operation, i.e., the temperature can again fall below the transition temperature of the superconductive material even though the current is maintained.
In the heavy current superconductor structure described in U.S. Pat. No. 4,195,199, the stabilization of the superconducting elements is achieved by also arranging special stabilizing elements of normally conducting material parallel to the superconducting elements. These stabilizing elements and the superconducting elements are twisted around a ribbon-shaped carrier body which may consist, for instance, of a material of high mechanical strength such as alloy steel. The elements are fastened on this ribbon. Adjacent superconducting and stabilizing elements of this heavy current superconductor structure are in intimate electrical and thermal contact with each other, which is obtained for instance, due to a joint hot deformation for shaping the conductor structure into a flat cable. The known heavy current superconductor structure therefore has a low transversal resistance so that it has correspondingly high losses in time-varying magnetic fields. Also, in this heavy current superconductor structure, the necessary cross sectional area of normally conducting metal is several times larger than the superconductor area required for transporting the current. The average current density of this conductor structure is therefore limited accordingly.
It is therefore an object of the present invention to improve the heavy current superconductor structure of the type mentioned at the outset in such a way that its requirement for normally conducting stabilizing metal is reduced, the requirements as to cooling are diminished and, nevertheless, reliable and low-cost operation is ensured even in applications in alternating fields. In addition, this conductor should be of relatively simple design.